SNOW-950923 Flaky test fix (#870)

### Description
Timeout delta increased to verify Login Request Timeout falls into
expected range.

### Checklist
- [x] Code compiles correctly
- [x] Code is formatted according to [Coding
Conventions](../CodingConventions.md)
- [x] Created tests which fail without the change (if possible)
- [x] All tests passing (`dotnet test`)
- [x] Extended the README / documentation, if necessary
- [x] Provide JIRA issue id (if possible) or GitHub issue id in PR name

Snowflake.Data.Tests/IntegrationTests/SFConnectionIT.cs

@@ -401,7 +401,7 @@ public void TestLoginTimeout()
                         ((SnowflakeDbException)e.InnerException).ErrorCode);
                 }
                 stopwatch.Stop();
-                int delta = 10; // in case server time slower.
+                int delta = 15; // in case server time slower.
 
                 // Should timeout before the defined timeout plus 1 (buffer time)
                 Assert.LessOrEqual(stopwatch.ElapsedMilliseconds, (timeoutSec + 1) * 1000);